1. Field of the Invention
This invention relates to a rubber composition suitable for use in a tire tread having a low rolling resistance, a high wet skid resistance and an excellent processability.
2. Description of the Prior Art
Lately, rubber materials having a low rolling resistance and a high skid resistance on wet road surface (wet skid resistance) have strongly been demanded as a rubber for tire tread in order to meet the requirements on low fuel consumption and running safety of automobile vehicles. Since these properties are conflictive to each other, however, rubbers simultaneously satisfying these properties are not proposed up to the present. For this reason, a blend of different rubbers has been used for harmonizing these properties. For instance, rubber blends of styrene-butadiene copolymer such as emulsion polymerized styrene-butadiene copolymer, solution polymerized styrene-butadiene copolymer or the like and polybutadiene such as high-cis polybutadiene, low-cis polybutadiene or the like have widely been used as a tire tread for passenger car. However, these rubber blends are not necessarily sufficient in the rolling resistance and wet skid resistance.
Therefore, it has been attempted to improve the rolling resistance, fracture properties and wear properties by introducing copolymer-metal bond into diolefin copolymer. In this connection, there are proposed conjugated diolefin copolymers having copolymer-metal (Sn, Si, Ge, Pb etc.) bond by using an organolithium initiator (Japanese Patent laid open No. 57-73,030, No. 58-122,939 and No. 58-122,947).
In the conjugated diolefin copolymers having copolymer-metal bond, however, there is yet room for improvement in the rolling resistance and processability as a rubber composition for tire.